Citigroup's former hedge-fund chief may have fallen for a scam out of a dime-store novel.

Dean Barr, who left Citi Alternative Investors after the bank purchased Vikram Pandit's Old Lane Partners and who now runs a private-equity firm, told a Florida court that he lost more than $1 million on a treasure-hunting expedition.

Barr said he was approached in 2010 by a Florida real-estate investor with an amazing story. Jay Miscovich told Barr that a drifter at a saloon in Key West had sold him a treasure map for $500—and that when Miscovich went to the site of the supposed wreck 40 miles from the island, he found a pile of emeralds on the sea floor. He even showed Barr bags of the emeralds he claimed to have recovered.

If the story sounds too good to be true, that's because it probably is: A federal court last year ruled that Miscovich's company had failed to prove the jewels were found on the sea floor, and in 2012 60 Minutes aired a report that said tests of the stones found some had been treated with a jeweler's polish that's only been around for 50 years.

For his part, Barr became suspicious after a few months, after the emeralds disappeared from a New York bank vault. He and his partner, Neil Ash, cut ties with Miscovich in 2011.

Barr is not a party to the current litigation, which pits Miscovich's company against another salvage company. Barr told the court that he was testifying "because I lost a significant amount of money and because I want to get to the bottom of why and who is responsible."

Even that may prove impossible: Miscovich, who was never charged with a crime, killed himself in October, and Steve Elchlepp, a former partner of both Miscovich and Barr, invoked his Fifth Amendment right against self-incrimination when called to the stand.

From the current issue of

We are accustomed to splitting trading into technical and fundamental buckets. Both involve crunching data; one set includes market fundamentals and the other pure price data. Alternative data is a third bucket that is gaining traction.